Field of the Invention
The present invention relates to a radiation detector that detects γ-ray and a radiation tomography imaging device having the same and particularly relates to a TOF-PET (Time-Of-Flight-Positron Emission Tomography).
Description of the Related Art
In a medical facility, a radiographic tomography imaging apparatus is equipped to perform an imaging of distribution of radiopharmaceuticals. The inventor sets forth a specific structure of such radiographic tomography imaging apparatus. A conventional radiation tomography imaging apparatus equips a radiation detector 51, having a scintillator in which scintillator crystals are arrayed as shown in FIG. 21, that are arranged circularly as shown in FIG. 22. The inventor sets forth briefly an operation of the radiation detector. When γ-ray is incident in the scintillator of the radiation detector, the γ-ray is converted to fluorescence by any one of the scintillation crystals. The detector recognizes which crystal generates the fluorescence and thereby can determine the incident location of the γ-ray (e.g., Patent Document 1).
Referring to FIG. 22, a detector ring 52 comprises such detectors arranged circularly. When the tomography imaging is performed, a subject is loaded inside the detector ring 52. It is given that the positron emission radiopharmaceuticals are accumulated in the emission-point p inside the detector ring. Radiation is frequently emitted from the emission-point p. The radiopharmaceuticals are labeled with a positron emission nucleus, so that the emitted radiation flying away in the opposite direction of 180° is the pair of γ-rays. Such pair is detected at the two different locations of the detector ring 52. It can be understood that the radiopharmaceuticals are located on the straight line (LOR) connecting both detection locations. However, the location of the emission-point p cannot be determined exactly yet. According to the conventional radiation fluoroscopy apparatus, the emission-point p is imaged by performing detection of such pair many times.
TOF-PET is an apparatus further developed from conventional apparatuses. If the emission-point p is located at the middle point of the LOR, the pair of γ-ray should be detected absolutely at the same time. If the emission-point p is located out of the middle point of the LOR, the detection time lag of the pair of the γ-ray takes place in the shift amount corresponding to such lag time. Specifically, if the time lag between two detected γ-rays were investigated, an approximate location of the emission-point p on the LOR could be obtained. The above is the principal of TOF-PET. According to TOF-PET, the more data can be obtained from one time detection of the pair of γ-rays, so that the more clearly sharp imaging can be performed.
Despite such TOF-PET, it is difficult to accurately determine the location of the emission-point p, at which the radiopharmaceuticals are accumulated. Referring to FIG. 23, accordingly to TOF-PET, the detection of the pair of γ-rays just only one time can provide the information indicating that the emission-point p is just around area surrounded by the broken lines.